The race by companies to develop autonomous cars is making rivals out of old friends as is evident from the exit of Alphabet’s senior executive David Drummond from the board of Uber Technologies.

Alphabet is an investor in Uber through its venture capital arm GV, and from all appearances will continue to stay so. But it had become increasingly evident that the ride-hailing company’s efforts to build self-driving cars would put it in conflict with the aims of the Google Self-Driving Car Project, which has been one of the pioneers in the development of these autonomous vehicles.

On Monday, Alphabet said Drummond, its senior vice president for corporate development, had recently quit the board of Uber. GV will continue to be an investor in the ride-hailing company.

"I recently stepped down from Uber's board given the overlap between the two companies,” Drummond said in a statement issued on Monday. “GV remains an enthusiastic investor and Google will continue to partner with Uber,” Drummond added. He wished Uber CEO Travis Kalanick all the best for the future.

The development comes ahead of tests of self-driving cars carrying ride-hailing passengers, planned by Uber later this month on the streets of Pittsburgh in the U.S. A number of car and component makers are developing technology for self-driving cars that they are targeting at ride-hailing companies, and there have been rumors that Google may also target this market.

Ford said this month that it intends to have a high-volume, fully autonomous vehicle in commercial operation in a ride hailing or sharing service by 2021. General Motors has also invested US$500 million in ride-hailing company Lyft in a deal that could see them jointly developing a network of on-demand autonomous cars. Earlier on Monday, The Information reported that Uber had shut out Drummond from attending board meetings, quoting three people briefed about the arrangement.

Google cars have self-driven over 1.5 million miles and are out on the streets of cities like Mountain View, California and Austin, Texas.